Vent pipes employed in connection with refinery sewer systems must draw air easily to prevent vacuum lock. Increasingly stringent environmental regulations have created a need for vent pipes to be sealed against evaporative pollution of the outside atmosphere. Refinery sewer systems employ a variety of ordinary water seals, such as S-traps, P-traps and other water seals in various locations of the sewer system. These arrangements are not for the purpose of venting air into the sewer system and, in fact, it is imperative that the typical water traps remain full of water to effectively prevent emissions from the sewer system into the ambient atmosphere. In the absence of a vent pipe or vent pipes elsewhere in the system, low pressure episodes in the sewer system can suck the water from the water traps and destroy the effectiveness insofar as gaseous emission prevention is concerned.